EXAMINATION OF BUOYANCY DRIVEN VENTILATION DESIGN USING THE CHARACTERISTICS OF OPENING RATIO OF NATURAL VENTILATION OPENING: Study on the performance evaluation of natural ventilation control in office buildings (Part 3)

As natural ventilation significantly contributes to energy savings and enhances comfort, it has been adopted in recent times in many buildings. However, there may be issue with natural ventilation such as the occurrence of low temperature environment; hence, the natural ventilation rate must be set to appropriate value. In the previous study, the authors had proposed a new simulation tool that can be estimate the effect of natural ventilation control that includes the lower limit of room temperature by adjusting the “opening ratio”. However, it is difficult to vary the opening ratio continuously. Thus, the authors notice that there is a logical possibility that the opening ratio is used to set an appropriate effective opening area of the natural ventilation. In this paper, the authors examined an appropriate method for setting the effective opening area of natural ventilation opening and the lower limit of outdoor temperature using the lower limit of room temperature control calculator. First, as an example of the simulation results obtained by adjusting the opening ratio, the time variation diagram for the representative day, the air change rate, and the room temperature are presented. Although the air change rate is reduced by adjusting the opening ratio, it is possible to reduce the duration for which the lower limit of room temperature is at the set value or less. Furthermore, the authors performed calculations for 20 cases to understand the factors that influence the value of the opening ratio. It was found that the internal heat gain, the lower limit of the set value of room temperature and the number of floors influence the value of the opening ratio, and that the lower limit of the set value of room temperature has a significant influence. The details of this calculation are given in chapter 4. Next, as it is difficult to vary the opening ratio continuously in an actual building, the effective opening area of the natural ventilation opening and the method of setting the lower limit of outdoor temperature were examined to obtain the same result as in the case when the calculator with adjusting the opening ratio. The authors presented the correlation between the outdoor temperature and opening ratio from the simulation results obtained in chapter 4, and studied the method of setting the effective opening area of the natural ventilation opening and the lower limit of outdoor temperature; thus, it was possible to reduce the duration for which the temperature was below the lower limit of the set value of room temperature. The details of this calculation are given in first half of chapter 5. Finally, the method of setting the effective opening area of the natural ventilation opening, depending on the floor, was studied to reduce the difference between the air change rates in different floors. By adopting a setting method that increases the effective opening area of the natural ventilation opening toward the upper floor, the difference between the air change rates in different floors could be reduced, and the duration for which the temperature is below the lower limit of the set value of room temperature setting could be reduced. In future study, the authors would like to examine the natural ventilation design method under the condition when wind pressure is applied.